This invention relates to a hot-melt sheet for holding and protecting semiconductor wafers, that is used in processing semiconductor wafers comprising silicone, gallium-arsenic, or the like, and a method for applying the same. More particularly, it relates to a hot-melt sheet that is applied by heat-fusion to a surface of a semiconductor wafer on which a circuit pattern has been formed (hereinafter referred to as a xe2x80x9cpatterned surfacexe2x80x9d for simplicity) in polishing and grinding a back surface thereof, thereby protecting the patterned surface and, at the same time, holding the thus thinned semiconductor wafer, and a method for applying the same.
Where a semiconductor wafer is polished and ground on its surface opposite a surface having a circuit pattern formed thereon, the patterned surface must be protected from damage or contamination with grinding dusts, grinding water, etc. Further, the semiconductor wafer itself is thin and brittle, and also a patterned face of the semiconductor wafer has an uneven form, there is the problem that semiconductor wafers tend to be broken even if a slight external force is applied thereto.
In order to attempt protection of the patterned face of semiconductor wafers and prevention of them from breakage in processing the semiconductor wafers, a method of applying a pressure-sensitive adhesive sheet to the patterned surface of semiconductor wafers is known. For example, JP-A-61-10242 discloses a film for processing semiconductor wafers which comprises a substrate sheet having a Shore D hardness of 40 or less and a pressure-sensitive adhesive layer formed on the surface thereof. (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d.) Further, JP-A-61-260629 discloses a film for processing wafers which comprises a substrate film having a Shore D hardness of 40 or less, an auxiliary film having a Shore D hardness exceeding 40 laminated on one surface of the substrate film, and a pressure-sensitive adhesive layer formed on the other surface of the substrate film.
In recent years, roughness on a patterned surface of semiconductor wafers is increasing. For example, wafers provided with a polyimide film have the roughness of about 1 to 20 xcexcm. Further, bad marks for recognizing defective semiconductor chips have roughness of about 10 to 70 xcexcm. Also, height of bumps formed on patterned electrodes is about 20 to 200 xcexcm. For those reasons, in the method of using conventional pressure-sensitive adhesive sheet, the conventional adhesive sheets cannot follow up the unevenness, resulting in insufficient adhesion between the pressure-sensitive adhesive and the wafer surface. As a result, peeling of sheets, invasion of grinding water or foreign matters into the patterned surface, processing errors, dimpling, or the like may occur, and also wafers may break, in processing wafers.
Accordingly, one object of the present invention is to provide a sheet for holding and protecting semiconductor wafers, which can closely follow up unevenness on a wafer surface even if the roughness thereof is large, and a method for applying the same.
Another object of the present invention is to provide a sheet for holding and protecting semiconductor wafers, which has excellent release properties from the wafer surface and small staining properties to the wafer surface, and a method for applying the same.
Still another object of the present invention is to provide a sheet for holding and protecting semiconductor wafers, which has excellent application workability and also has high holding and reinforcing properties to wafers, and a method for applying the same.
As a result of extensive investigations to achieve the above-described objects, it has been found that a sheet provided with a hot-melt layer having a specific melting point well follows up unevenness on a semiconductor wafer surface even if the roughness is large and, after completion of the grinding process, the sheet can easily be released from the wafer surface without staining the same. The present invention has been completed based on this finding.
According to a first embodiment of the present invention, there is provided a hot-melt sheet for holding and protecting semiconductor wafers by applying to a surface of a semiconductor wafer to thereby hold and protect the semiconductor wafer in processing the semiconductor wafer, the sheet comprising a hot-melt layer A having a melting point of 105xc2x0 C. or lower.
According to a second embodiment of the present invention, there is provided a method for applying a hot-melt sheet for holding and protecting semiconductor wafers to a surface of a semiconductor wafer, which comprises laminating the hot-melt sheet for holding and protecting semiconductor wafers as described above on the semiconductor wafer, and then heating the hot-melt sheet to apply the sheet to the wafer
In the above method, where a pressure-sensitive adhesive layer B is formed on one surface of the hot-melt layer A, the resulting sheet is laminated in such a manner that the pressure-sensitive adhesive layer B faces the semiconductor wafer.
FIG. 1 is a schematic sectional view showing one example of the hot-melt sheet for holding and protecting semiconductor wafers according to the present invention;
FIG. 2 is a schematic sectional view showing another example of the hot-melt sheet for holding and protecting semiconductor wafers according to the present invention;
FIG. 3 is a schematic sectional view showing still another example of the hot-melt sheet for holding and protecting semiconductor wafers according to the present invention;
FIG. 4 is a schematic sectional view showing further example of the hot-melt sheet for holding and protecting semiconductor wafers according to the present invention; and
FIG. 5 is a schematic sectional view showing still further example of the hot-melt sheet for holding and protecting semiconductor wafers according to the present invention.